Pencil lead and the art of making the same



Patented Mar. 30, 1937 UNITED STATES PENCIL LEAD AND THE ART OF MAKINGTHE SAME

Adolf Pischel, New York, N. Y., assignor to Eagle Pencil Company, NewYork, N. Y., a corporation 01' Delaware No Drawing. ApplicationSeptember 10, 1934, Serial No. 743,411

Claims.

My present invention relates to the art of pencil leads, more especiallyto those of the unfired type, ordinarily used for colored leads.

Among the objects of the invention are to provide a lead of the abovetype, superior in writing or marking characteristics, by which eveninferior and inexpensive pigments become readily and uniformlydistributed on the paper or other writing surface with a minimum offrictional drag, in writing.

Another object is to provide a method for producing a pencil lead of theabove type, with the use of substantially conventional apparatus and bya series of steps readily executed without the exercise of a high orderof skill.

A feature of the invention is the intimate dispersion throughout thebody of the lead, made up essentially of conventional filler, pigmentand binder, of waxy ingredients, interspersed intimately and inrelatively large proportions by weight.

Where it is attempted merely to impregnate in hot wax, a lead made upwholly of filler, pigment and binder, the wax does not readily penetrateto the interior or core of the lead, especially where case hardened clueto extrusion through the die,

and since it is the core which chiefly functions as the writing point,the desired uniformity of marking and ease of slippage is not therebyattained.

On the other hand, if wax is incorporated with the batch of filler,pigment and binder, which is extruded through a die in making the lead,the individual particles of the pigment and binder do not becomethoroughly coated with wax, and since interstices are readily formed asa result of the escape of water in the drying operation in the hot airfurnace, the lead lacks the mechanical strength of a solid structure.

By the present invention, comminuted wax substantially powdery orflour-like in character, is incorporated as an element of the batch orfiller, pigment and binder, and after the lead including suchingredients is extruded through the die, the lead thus formed issubjected to an impregnating operation in a molten Wax. Preferably, the

lead after extrusion is subjected to a drying operation in a furnacethrough which heated air is circulated and such drying is conducteduntil the moisture content of the lead is very low, and the hot-Waximpregnation operation is conducted only after such drying.

The leads with the wax initially incorporated therein become porous witha multiplicity of minute irregular passages, fissures or intersticestherein, formed by the moisture escaping from the interior of the leadin the drying operation.

According to my invention, the leads previously dried may be placed in avacuum chamber, to exhaust the air from the minute fissures, or passagesin the lead, whereupon the molten wax is admitted and will penetratethese fissures, en-

tering into the innermost recesses of the lead and incidentallypartially melting or softening the wax initially incorporated in thelead, thereby to cause a much more intimate admixture of the wax withthe harder particles making up the body of the lead.

Regardless whether vacuum is used or not, the lead is preferably keptunder the wax for some hours, to assure complete impregnation, whereuponthe wax is allowed to cool down to near, but not quite the temperatureof hardening, at which temperature the leads which are preferablysubmerged within a perforated basket are removed from the wax and arepermitted to cool in air to room temperature.

It is preferred, prior to submerging the leads in the hot impregnatingwax to heat said leads substantially to the temperature of said wax,thus driving out a large part of the air present in the pores of thelead and also to avoid the possibility of chilling the wax.

While it is within the scope of my invention to use the same waxcomposition both as the initial ingredient of the leadbatch and as theimpregnating medium, it is preferred to use different waxes, each mostsuited for its intended purpose.

As an ingredient of the initial batch, it is preferred to use stearicacid, spermaceti, Japan wax,

bayberry or a mixture or blend of two or more of such substances. Thiswax or these waxes are incorporated in finely comminuted form ofsubstantially flour-like consistency, these waxes being of the type thatcan readily be brought into that state of fine subdivision. The wax usedfor impregnation is preferably a blend of carnauba wax with eithertallow or stearic acid, or Japan wax preferably in equal parts, saidblend being found small proportion of calcium steal-ate. Thereupon,

the binder is added preferably in. the form of water soaked aglutinantof etherlzed cellulose according to the teachings of the copending ap- 5plication of Isidor Chesler, Serial No. 720,573, filed April 14, '1934.The mixture of the batch is now compressed and kneaded by use of aseries of appropriate machines for securing a homogeneous intimatelymixed and tough dough, which is thereupon filled into cylinders andforced through perforated plates and recompressed. Finally .the

dough is forced through dies of the proper calibre v to produce therod-like lead product.

The drying operation before the wax impregnation is preferably performedin racks, according to familiar practice, including covering the leadswith boards to prevent warping thereof. The leads are first dried atroom temperature, then maintained for a week or more in a drying-chamherof 120 degrees F. with the application of air in pregnation in the waxbatch in which they are allowed to cool nearly to the congelationtemperature of the wax are removed from the bath and cooled in air.Thereupon the leads are tested for strength, grade and quality andincorporated in By the process set forth, the resultant lead has a highproportion of wax or grease incorporated in it, the combination ofpowdered wax initially introduced, with the wax entering by impregnationbeing as high as 18 to 20 per cent of the weight of thelead. As aresult, the individual particles are quite thoroughly greased, clearinto the core of the lead and by reason of the u'nctuous character ofthe added waxy ingredients, including the calcium stearate, the lead isso slipping in character, that it takes readily to the paper and uniformpressure will make a uniform line of uniform color and weight. By theprocess set forth, theproduct admits of use of relatively inferiorpigments with results at least as good as those attained by olderprocesses, even with the use of expensive pigments.

It will thus be seen that there is herein described a method and productin which the several featuresof this invention are embodied, and whichapparatus in service attain the various objects of the invention and arewell suited to meet the requirements of practical use.

As many changes could be made inthe above construction, and manyapparently widely different embodiments of this invention could be madewithout departing from the scope thereof, it

is intended that all matter contained in the above description shall beinterpreted as illustrative and not in a limiting sense.

75 with a comminuted wax. extrudlns the individual lead, which co wiseconventional mix. including a filler, a pigthe pencil, as by gluing intothe usual wooden case.

Having thus described my invention, what I g aovaaas leads and thensubjecting them under best team impregnating bath inmolten wax. a 3. Themethod of'preparing'a pencil lead. whichbinder with comminuted wax,extruding the lead :rods, subjecting the latter to a drying operation.consists inintimatelyadmixing mien-pigment and 4. The method of makingan unfired writing in incorporating in the otherment and a binder, acomminuted wax, then subjecting the lead rods to a drying operation andfinally subjecting'the dried lead rods to heat,

thereby softening the wax incorporated therein and at the same timeapplying molten wax from the exterior of the lead rod.

5. 'The method of making a pencil lead of the unfired type. whichconsists in incorporating with the mixture of filler, pigment andbinder, comminuted wax'of flour-like consistency, including one or moreingredientsof the group made up of stearic acid. Japan wax, spermaceti,and bayberry, and after completing the lead from these ingredientsimpregnating said lead in a bath of molten wax. I

6. The method of making a pencil lead of the unfired type, whichconsists in incorporating with the mixture of filler, pigment andbinder. a comminuted wax of flour-like consistency, including one ormore ingredients of the group consisting of stearicacid, Japan wax,spermaceti and bayberry, and after completing the lead from theseingredients, impregnating said lead in a bath of molten wax, said bathcomprising a blend of carnauba wax with one or more members of the groupconsisting of tallow and stearic acid.

7. The method of making a pencil lead of the unfired type, whichconsists in incorporating with the mixture of filler, pigment andbinder, comminuted wax of flour-like consistency including one or moreingredients of the group consisting of stearic acid. Japan wax,spermaceti and bayberry, then drying the leads in circulating heated airuntil the moisture content thereof has been greatly reduced and finallyimpregnating said dried lead in a bath. of molten wax. said bathcomprising a blend of carnauba wax with one or more members of thegroup, consisting of tallow and stearic acid.

8. The method of. making a'pencil lead of the unfired type, whichconsists in incorporating with the mixture of filler, pigment andbinder, a comminuted wax, drying the leads until the moisturecontentthereof has been greatly reduced, preheating the leads tosubstantially the temperature of a bath of molten impregnating wax andthen submerging the leads in said impregnating wax, and removing theimpregnated leads from the wax before the latterhas hardened.

9..The method of making a pencil lead of the unfired type, whichconsists in incorporating with the mixture of filler,- pigment andbinder, a comminuted'wax, drying the leads until the moisture contentthereof has been greatly reduced, subjecting the leads to vacuum toremove air from the interstices thereof, then impregnating the leads inmolten wax after preheating the leads to substantially the temperatureof said molten wax.

10. The met of making a pencil lead of the unfired type. w I ch consistsin incorporating with the mixture of-filler, pigment and bindercomminuted wax. drying the leads until the moisture content thereof hasbeen greatly reduced, and then impregnating the leads in molten wax.

11. An unfired pencil lead comprising filler, pigment and binder, havingintimately interspersedtherein, a large percentage of wax thoroughlypermeating the lead to its core, said wax includin particles thereofadmixed with the filler, and particles substantially filling minuteinterstices left in the interior as a consequence of the usual dryingoperation.

12. An unfired pencil lead comprising filler, pigment and binder havingintimately interspersed therein, a large percentage of wax thor-.-oughly permeating the lead to its core, said wax including particlesthereof admixed with the filler, and particles substantially fillingminute interstices left in the interior as a consequence of the usualdrying operation, the exterior of the ,lead being porous.

13. An unflred pencil lead comprising filler, pigment and binder withadmixed wax substantially throughout the body and in the core of thelead and additional wax impregnating interstices formed in theconventional drying of the lead.

14. An unfired lead comprising filler, pigment and binder and waxsubstantially homogeneously mixedthroughout the mass, said leadimpregnated with a wax of difierent composition filling intersticesformed in the conventional drying of the lead and substantially bondedto the wax incorporated with the original mixture of the lead. 15. Anunfired pencil lead including a filler, a pigment, and a binder, havingadmixed therewith, a comminuted wax including one or more of ADOLFPISCHEL.

